Volume 96, Issue 2, 15 July 2004
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
96(2004); http://dx.doi.org/10.1063/1.1762712View Description Hide Description
Ions in cathodic arc plasmas have high velocities attained by acceleration at cathode spots. Among other techniques, two time-of-flight setups had previously been used to determine ion velocities. These measurements showed significant discrepancies especially for some light cathode materials like carbon. To reconcile the differences, a thorough investigation was conducted using carbon as the cathode material. It is shown that systematic errors occur when the ion sourcetime-of-flight system is not operated near perveance-matching conditions. The extracted ion beam is not parallel but divergent, and the Faraday cup detector measures only a fraction of the beam. In contrast, plasma source experiments without ion extraction are free of such distortions. In the absence of an external magnetic field, the average carbon ion energy has been determined to be in the range 18.5–20.5 eV for arc currents in the range 100–600 A, in agreement with previous plasma sourcemeasurements and other literature data.
96(2004); http://dx.doi.org/10.1063/1.1759397View Description Hide Description
Plasma electron density and atomic population densities in the plasma plume produced by a laser ablation of aluminum metal were determined in various ambient gases at relatively high pressures. The method is based on the fit of a spectral line profile of emission to the theoretical spectrum obtained by one-dimensional radiative transfer calculation. The electron density was higher for a higher ambient gas pressure, suggesting the confinement of the plume by an ambient gas. The electron density also depends on the type of ambient gases, i.e., it increased in the order while the atomic population density is almost independent of the type of ambient species and pressure. The population densities of the upper and lower levels of the transition were compared, and the ratio between their spatial distribution widths was calculated. These results provide valuable information regarding the confinement of the plume by the ambient gas and give insight into the time evolution of the plume.
96(2004); http://dx.doi.org/10.1063/1.1759790View Description Hide Description
A stationary, macroscopic model [E. Ahedo, J. Gallardo, and M. Martı́nez-Sánchez, Phys. Plasmas 10, 3397 (2003)] is used to carry out parametric investigations on the effects of (i) the discharge voltage, (ii) the gas flow rate, (iii) the axial gradient of the magnetic field, and (iv) the chamber length on the Hall thruster performances and the axial structure of the plasma discharge. The high-thrust and high-specific-impulse modes for dual-mode thrusters are compared too. The results of the simulations agree well with the main tendencies observed in different experiments. The interaction among the several physical phenomena is discussed and useful scaling laws are proposed. Special attention is paid to understand (i) the adjustment of the magnetic field strength with the discharge voltage for optimum operation, (ii) the effect of the magnetic field shape, (iii) the dimensions of the different regions of the discharge, and (iv) the parameter trends needed to increment the propulsive and ionization efficiencies (the product of which determines the thrust efficiency).
Characteristics of plasma display panel with ridged dielectric and hollow gap between sustain electrodes96(2004); http://dx.doi.org/10.1063/1.1756694View Description Hide Description
This article presents a front panel structure for an alternating currentplasma display panel (AC-PDP) based on a ridged transparent dielectric layer and long hollow gap between the sustain electrodes. The suggested structure can reduce a firing voltage and sustain voltage than a conventional AC-PDP due to a strong electric field between the sustain electrodes. Experiments were conducted with various Xe contents from 10% to 50% at a gas pressure of 450 Torr, and the results confirmed that the ridged dielectric structure reduce the firing and sustain voltages by about 74 and 79 V at 10% Xe content than a conventional structure with 10% Xe content, respectively. Also, the proposed structure improve the luminous efficiency and luminance by about 50.9% and 33%, respectively, with a 50% Xe content when compared to a conventional structure with a 10% Xe content at a similar driving voltage.